Scanning unit of an optical position measuring arrangement and position measuring arrangement having this scanning unit

ABSTRACT

A scanning unit, by which a scale, which is movable in relation to the scanning unit in a measuring direction, can be optically scanned. The scanning unit including a detector arrangement and a transparent support having a first surface and a second surface, wherein the detector arrangement is arranged on the second surface. The scanning unit further including a transparent cover plate, which is fastened on the first surface of the transparent support and includes a shielding device for shielding the detector arrangement against electromagnetic fields.

RELATED APPLICATIONS

Applicant claims, under 35 U.S.C. § 119, the benefit of priority of thefiling date of Nov. 8, 2007 of a German patent application, copyattached, Serial Number 10 2007 053 137.2, filed on the aforementioneddate, the entire contents of which is incorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention relates to a scanning unit of an optical positionmeasuring arrangement, by which a scale, which can be moved in relationto it in the scanning direction, can be optically scanned, as well as toa position measuring arrangement having this scanning unit.

2. Background Information

Such scanning units and position measuring arrangements are designed inthe form of linear measuring devices having a linear scale, or as rotarymeasuring devices, having a disk-shaped or drum-shaped scale. They arein particular employed in processing machinery for measuring therelative movement of a tool with respect to a workpiece to be worked, inconnection with robots, coordinate measuring machinery, and increasinglyin the semiconductor industry.

In many applications, the position measuring arrangement is exposed toelectrical fields, in particular to interfering electrical alternatingfields, which have an effect on electrically conducting elements of thescanning device and cause electrical interferences and a resultanterroneous position detection.

It is proposed in DE 44 02 554 A1 to shield the detector arrangementagainst electromagnetic interference fields by a transparent,electrically conducting shielding body, which is connected to groundpotential.

In actual use it has been shown that in connection with thisconstruction the production of the shielding device and the electricalcontact with ground potential is difficult.

OBJECTS AND SUMMARY OF THE INVENTION

It is therefore an object of the present invention to create a compactand dependably shielded scanning unit, or respectively positionmeasuring arrangement.

This object is attained by a scanning unit, by which a scale, which ismovable in relation to the scanning unit in a measuring direction, canbe optically scanned. The scanning unit including a detector arrangementand a transparent support having a first surface and a second surface,wherein the detector arrangement is arranged on the second surface. Thescanning unit further including a transparent cover plate, which isfastened on the first surface of the transparent support and includes ashielding device for shielding the detector arrangement againstelectromagnetic fields.

This object is also attained by an optical position measuringarrangement including a scale and a scanning unit, which is movable in ameasuring direction relative to the scale. The scanning unit includes adetector arrangement and a transparent support having a first surfaceand a second surface, wherein the detector arrangement is arranged onthe second surface and wherein the first surface of the transparentsupport faces the scale and the second surface of the transparentsupport faces away from the scale. The scanning unit further includes atransparent cover plate, which is fastened on the first surface of thetransparent support and includes a shielding device for shielding thedetector arrangement against electromagnetic fields.

The advantage of the present invention lies in that it is possible torealize a compact and dependably shielded scanning unit, or respectivelyposition measuring arrangement.

It is intended by exemplary embodiments represented in the drawings toexplain the concept on which the present invention is based and furthercharacteristics and variants of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Shown are in:

FIG. 1 shows a longitudinal section through an embodiment of an opticalposition measuring arrangement in accordance with the present invention;and

FIG. 2 shows a perspective representation of a portion of an embodimentof a base body of an embodiment of a scanning unit used with theposition measuring arrangement of FIG. 1 in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2 show an exemplary embodiment of an optical positionmeasuring arrangement. In this case, the position measuring arrangementis a linear measuring arrangement, having a linear scale 1 and ascanning unit 2, which can be moved relative to the scale 1 in themeasuring direction X. The scale 1 has a measuring graduation 3, whichcan be scanned by incident light, i.e. is reflecting, and which isscanned by the scanning unit 2. Here, the scanning unit 2 includes alight source 4, whose light impinges on the scale 1, is modulated thereby the measuring graduation 3 as a function of its position and isreflected onto a detector arrangement 6.

The detector arrangement 6 is arranged on a transparent support 5,namely on the surface 9 facing away from the scale 1. The transparentsupport 5 is made of an electrically insulating transparent material, inparticular, it is a plan-parallel glass plate with two surfaces 9, 10extending parallel with and located opposite each other. One of thesesurfaces 10 is facing the scale 1, in what follows, this surface 10 willbe called first surface 10. But the second surface 9 is facing away fromthe scale 1. The detector arrangement 6 is arranged on this secondsurface 9. Mechanical and electrical contact with the detectorarrangement takes place in a known manner by chip-on-glass technology,in that a strip conductor pattern 11 is formed by coating the secondsurface 9, by which contact surfaces (bond pads) of the detectorarrangement 6 are contacted via so-called bumps in accordance withflip-chip technology and face down. Spaces between the detectorarrangement 6 and the transparent support 5 are optionally filled withan under-filter, which contributes to the mechanical stabilization ofthe construction.

The transparent support 5 has a scanning grating 7, which includes in aknown manner of opaque areas and transparent areas arrangedalternatingly next to each other. The scanning grating 7 is used forforming several partial bundles of beams, which interact with themeasuring graduation 3 of the scale 1 and impact on the detectorarrangement 6 for generating position-dependent scanning signals, whichare phase-shifted with respect to each other. In the representedexample, the scanning grating 7 is arranged on the first surface 10 ofthe transparent support 5. This spatial arrangement has advantages inthe production, since the scanning grating 7 can be produced as aseparate coating independently of the strip conductor pattern 11embodied as a further coating. In a manner not represented, the scanninggrating can also be a part of the detector arrangement 6 by beingapplied in a manner known per se to the light-sensitive surfaces, or thelight-sensitive areas of the detector arrangement 6 are themselvesstructured as scanning gratings.

The transparent support 5 with the light source 4 and the detectorarrangement 6 is only schematically represented, a possible actualembodiment has been described in the magazine article F&M, 1996, 10,pages 752 to 756, for example.

The transparent support 5 with the detector arrangement 6 fastenedthereon is arranged in a recess 21 of a base body 20. This recess 21 ofthe base body 20 is covered by a transparent cover plate 15. The basebody 20 is electrically conducting by including itself of anelectrically conducting material or being coated with electricallyconducting material, and it shields the detector arrangement 6 againstelectromagnetic fields on five sides. The base body 20, or respectivelyits electrically conducting coating, can be connected in a particularlyeasy manner with a reference potential OV which, in the course ofinstalling the scanning unit 2 on a machine element whose position is tobe measured, takes place by a simple contact with this machine element.The cover plate 15 is provided with a shielding device 16 for shieldingthe still open side, i.e. the access opening for inserting thetransparent support 5 into the recess 21. This shielding device 16 isarranged on the surface facing the first surface 10 of the transparentsupport 5. In an advantageous manner, the cover plate 15 is also aplan-parallel glass plate.

If the scanning unit is inserted into an encapsulated position measuringarrangement, the base body 20 is the scanning carriage, which islongitudinally guided on the scale 1 in the measuring direction X viaguide elements (sliding bearings, rollers, ball bearings).

The shielding device 16 is a coating of the scanning plate 15 andincludes a transparent, electrically conducting material, in particularof indium tin oxide, also called ITO. This coating has been applied of alarge surface and shields the entire opening of the recess 21. It isalso alternatively possible for the shielding to be an electricallyconducting grating structure, which is embodied in such a way that, inconnection with the measuring graduation 3, it does not cause anyposition-dependent modulation and is transparent, at least partially, tothe scanning beam path.

The cover plate 16 is fastened to the first surface 10 of thetransparent support 5, in particular via a flat, thin, transparentlayer, for example in the form of a continuous or parallel, partiallyapplied transparent adhesive layer 8, or in the form of a thin oil filmacting as an adhesive film. The cover plate 15 projects, at leastpartially, laterally over the transparent support 5, and the shieldingdevice 16 is extended as far as this projecting area 15.1, so that itcan be used there for a simple and space-saving electrical contact withthe base body 20, as well as with the reference potential OV. Thiscontact, which is designed to be electrical and to have low impedance,takes place in a particularly simple manner in that a gap is createdbetween the support 26 and the projecting areas 15.1 of the cover plate15, into which an electrically conducting adhesive 23 is introduced overa relatively large surface. By the interposition of the adhesive 23, thelateral surfaces of the recess 21 thus constitute a support 26 for thecover plate 15 (detail represented in FIG. 2). At least one pocket 22,visible in FIG. 2, is provided on the base body 20 for the satisfactoryintroduction of the electrically conducting adhesive 23 between thecover plate 16 and the base body 20. The pocket 22 is used as a reservefor the adhesive 23, so that the latter can flow by means of capillaryaction into the gap between the cover plate 15 and the support 26 of thebase body 20.

The package including the transparent support 5 and the cover plate 15has been positioned aligned in the recess 21 of the base body 20. Tothis end, sides of the transparent support 5 cooperate with stops 24 ofthe base body 20. It is advantageous if only the transparent support 5is aligned on the base body 20 by means of several lateral stops 24, andthe cover plate 15 is here arranged over the entire circumference at adistance from the inner circumferential surfaces of the recess 21 of thebase body 20, which are located opposite the sides of the cover plate15. Redundancy in the positioning of the support 5 on the base body 20is prevented in this way.

For further securing the seating of the support 5 on the base body 20,it is fixed in place along its edges on the base body 20 by an adhesive25. The adhesive 25 is introduced through passages 27 in the base body20.

Still further electrical components for evaluating the electricalscanning signals provided by the detector arrangement 6 are located onthe support 5 in addition to the detector arrangement 6. It isparticularly advantageous if these components and the detectorarrangement 6 are together embodied in an opto-chip (ASIC). In that casethe term detector arrangement corresponds to the ASIC component.

A scale can also be scanned by transmitted light with the scanning unitin accordance with the invention. In this case the light source is notlocated on the transparent support, but on the other side of the scale.

The spatial arrangement of the cover plate 15 in the scanning gapbetween the scale 1 and the support 5 has the further advantage that thescanning gap is filled with a defined material and can be less affectedin an undefined manner by media, such as dust and fluids. Therefore thethickness of the cover plate 15 is selected to be such that the distancebetween the scale 1 and the support 5 is almost completely filled by thecover plate 15, but that the free relative movement between the scale 1and the scanning unit 5 in the measuring direction X for positionmeasurement is not hampered.

The foregoing description is provided to illustrate the presentinvention, and is not to be construed as a limitation. Numerousadditions, substitutions and other changes can be made to the presentinvention without departing from its scope as set forth in the appendedclaims.

1. A scanning unit, by which a scale, which is movable in relation tosaid scanning unit in a measuring direction, can be optically scanned,said scanning unit comprising: a detector arrangement; a transparentsupport comprising a first surface and a second surface, wherein saiddetector arrangement is arranged on said second surface; a transparentcover plate, which is fastened on said first surface of said transparentsupport and comprises a shielding device for shielding said detectorarrangement against electromagnetic fields.
 2. The scanning unit inaccordance with claim 1, wherein said shielding device comprises atransparent layer of an electrically conducting material.
 3. Thescanning unit in accordance with claim 2, wherein said electricallyconducting material comprises indium tin oxide.
 4. The scanning unit inaccordance with claim 1, wherein said transparent support comprises ascanning grating.
 5. The scanning unit in accordance with claim 4,wherein said scanning grating is formed on said first surface of saidtransparent support.
 6. The scanning unit in accordance with claim 1,wherein said second surface of said transparent support comprises acoating forming a strip conductor pattern, with which said detectorarrangement is brought into contact by flip-chip technology.
 7. Thescanning unit in accordance with claim 1, wherein said transparentsupport with said detector arrangement is arranged in a recess of a basebody, and said recess is covered by said transparent cover plate.
 8. Thescanning unit in accordance with claim 7, wherein said base body iselectrically conducting, and said shielding device is connected in anelectrically conducting manner with said base body.
 9. The scanning unitin accordance with claim 8, wherein said transparent cover platecomprises areas which laterally project past said transparent support.10. The scanning unit in accordance with claim 9, wherein said shieldingdevice is arranged on a surface of said transparent cover plate whichfaces said first surface of said transparent support.
 11. The scanningunit in accordance with claim 10, wherein said shielding device is inelectrical contact with said base body at said areas of said transparentcover plate.
 12. The scanning unit in accordance with claim 7, whereinsaid shielding device of said cover plate is in electrical contact withsaid base body by an electrically conducting adhesive.
 13. The scanningunit in accordance with claim 7, wherein a package comprising saidtransparent support and said transparent cover plate is positioned insaid recess of said base body in that sides of said transparent supportcooperate with stops of said base body.
 14. The scanning unit inaccordance with claim 13, wherein when said package is positioned insaid recess, said transparent cover plate is arranged at a distance frominner circumferential faces of said recess of said base body which arelocated opposite said sides of said transparent cover plate.
 15. Anoptical position measuring arrangement, comprising; a scale; and ascanning unit, which is movable in a measuring direction relative tosaid scale, wherein said scanning unit comprises: a detectorarrangement; a transparent support comprising a first surface and asecond surface, wherein said detector arrangement is arranged on saidsecond surface and wherein said first surface of said transparentsupport faces said scale and said second surface of said transparentsupport faces away from said scale; and a transparent cover plate, whichis fastened on said first surface of said transparent support andcomprises a shielding device for shielding said detector arrangementagainst electromagnetic fields.